This marks the tenth blackout at the facility during nearly three and a half years of Russian occupation, and the longest one to date.

For more than four months, the plant has relied on a single external power line, whereas before 2022 it had ten. This sole remaining 750-kilovolt line, running north to connect the plant with Ukraine’s energy system, was reportedly damaged about 1.5 kilometers from the site because of military action. The line was cut at 16:56 local time on September 23, according to both the Russian-installed plant management and the International Atomic Energy Agency (IAEA).

Since then, the plant has been powered by backup diesel generators. Electricity from either the external grid or the generators is vital for the plant’s internal systems — especially where cooling the nuclear fuel stored in the reactors and spent fuel pools is concerned. Without cooling, this fuel could overheat and melt, leading to a situation reminiscent of the 2011 Fukushima disaster in Japan.

However, the current blackout raises not only the risk of a radiation accident but also suspicions that it could be part of a Russian plan to reconnect the Zaporizhzhia plant to its own power grid.

Despite the danger and instability, the actual risk of a nuclear accident remains relatively low. The plant has enough diesel generators — twenty in total. Immediately after the 750-kV line was cut on September 23, eighteen generators automatically kicked in, while two were under maintenance. As in similar incidents before, staff gradually reduced the number in operation to those required to supply essential systems, conserving fuel. As of September 30, eight generators remain running.

Russian officials have repeatedly informed the IAEA that the plant maintains enough diesel fuel on site to power the emergency generators for at least 20 days. Deliveries of diesel are reportedly ongoing, and additional shipments could be arranged if necessary. This allows the plant to remain in this emergency mode for quite some time.

Even in the event of generator failure — due to breakdowns or fuel shortages — there would still be enough time to act before the nuclear fuel overheats and begins to melt.

All six reactors have been shut down for over three years, and the residual heat from radioactive decay — which decreases exponentially over time — is now much lower than immediately after shutdown. Based on data used in Bellona’s 2024 report on the potential restart of the plant, current residual heat output per reactor does not exceed 800 kilowatts. Including spent fuel in cooling pools, total heat generation per reactor unit is no more than 2.5 megawatts (a conservative estimate — the real value is likely lower).

This means that even if all cooling systems were to fail completely, the remaining water in the reactor buildings would continue to cool the fuel through evaporation for at least two to three weeks — enough time to take emergency measures and prevent a major accident.

Only if nothing were done at all would the fuel begin to overheat and melt, potentially damaging the reactor vessel and allowing molten material to reach the lower levels of the unit — and theoretically, the ground and surrounding environment. Some radioactive materials could also be released into the atmosphere, either through pressure relief from the reactor’s containment or as a result of hydrogen explosions if recombination systems fail.

For now, however, there is enough time — and enough technical options — to prevent any of these scenarios, beginning with the repair of the damaged power line and the maintenance of the backup generators.

So why hasn’t Russia repaired the line, and could it be using this situation as a pretext to switch the plant over to its own power grid?

First, the power line could have been repaired long ago. According to the IAEA and the Russian occupation authorities at the plant, the break occurred about 1.5 kilometers from the plant on territory controlled by n troops along the left bank of the former Kakhovka Reservoir. It seems unlikely that for more than a week, repair crews — who have fixed similar line breaks in a matter of hours in the past — have been unable to do so.

Additionally, satellite imagery analysis conducted by McKenzie Intelligence Services for Greenpeace found no evidence of shelling or visible damage to the transmission line in question, calling into doubt the official Russian explanation for the outage.

As Bellona noted in its 2024 report on the possible restart of the ZNPP, connecting the plant to Russia’s power grid — or to that of the occupied territories — would be a necessary first step for Moscow in preparing to restart the facility.

This would not mean an immediate restart. Major technical issues remain unresolved: restoring water supplies, reloading nuclear fuel, and expanding transmission lines to carry power from the plant. Despite some progress—such as preparations for new pumping stations and transmission routes—restarting even one reactor is still months away.

For now, the likely goal would be simply to connect the plant to Russia’s grid to provide the few megawatts of electricity needed for safety systems. Under the pretext that the repair of the Ukrainian connection is impossible due to combat operations, Russia could attempt such a switch. In June this year, Russia informed the IAEA via diplomatic note that it had developed exactly such a plan in case of a plant blackout.

This could then be presented as a humanitarian step — “saving the plant from a nuclear accident” — a message that might find a sympathetic audience within the IAEA and among an anxious international public.

For that reason, the current situation must be assessed soberly: the immediate danger to the plant is serious but manageable. The greater danger lies in Moscow’s potential use of the crisis to justify reconnecting the plant to its own grid — portraying itself as the savior preventing a nuclear disaster.

In reality, any step toward integrating the Zaporizhzhia plant into Russia’s power system would only worsen its strategic situation, give Moscow additional leverage, and bring a potential restart closer — a move that, amid ongoing fighting, would itself sharply increase the risk of a nuclear accident.

Under no circumstances should the Zaporizhzhia Nuclear Power Plant be reconnected to the Russian grid or restarted. The facility must return to the full control of its rightful owner — Ukraine.

Bellona calls on the IAEA and other international organizations not to assist or legitimize Russia’s unlawful plans to integrate the Zaporizhzhia NPP into its own energy system or to normalize the current occupation status.